1. Field of the Invention
The present invention relates to an isolated primary circuit regulator, and more particularly to an isolated primary circuit regulator having a control circuit.
2. Related Art
In current electronic devices, in order to meet the safety requirements, a power supply is required to be capable of providing a stable output voltage and a stable output current. Under such conditions, the power supply is mostly composed of a transformer, and a switching regulator is disposed at a primary side of the transformer to adjust the output current. However, among transformer-related designs disclosed in the prior art, the technology of disposing the switching regulator at the primary side of the transformer still cannot accurately control the output current of the power supply. Therefore, an additional current loop is required at a secondary side of the power supply, so as to achieve a constant current curve with linear characteristics. As a result, the manufacturing cost is greatly increased. Therefore, how to accurately control the output current of the power supply while reducing the cost is indeed a research subject of interest.
Currently, the method of adjusting the output current of the power supply by disposing the switching regulator at the primary side of the transformer is characterized by detecting a primary-side switching voltage signal and a discharge time of a secondary-side switching current. The primary-side switching voltage signal is generated at the primary side of the transformer, and the secondary-side switching current is generated at the secondary side of the transformer. For related technologies and studies, reference is made to ROC Patent No. I277852, which discloses a switching control circuit controlling output current at the primary side of a power converter, including as follows: A waveform detector generates a current-waveform signal. A discharge-time detector detects a discharge-time of a secondary side switching current. An oscillator generates an oscillation signal for determining the switching frequency of the switching signal. An integrator generates an integrated signal by integrating an average current signal with the discharge-time. The average current signal is generated in response to the current-waveform signal. The time constant of the integrator is correlated with the switching period of the switching signal, therefore the integrated signal is proportional to the output current. An error amplifier amplifies the integrated signal and provides a loop gain for output current control. A comparator controls the pulse width of the switching signal in reference to the output of the error amplifier. The technical means disclosed in the patent uses a current sensing terminal to directly detect a primary-side switching voltage signal generated at the primary side of the transformer of the power supply. However, it should be noted that, although the output current of the power supply can be stabilized and adjusted by the technical feature, a voltage spike caused by sudden switching of a switch would occur, resulting in false determination of the switching regulator. Moreover, the integrator and the waveform detector increase the manufacturing cost of the switching regulator.